JP5516464B2 - Liquid ejection device - Google Patents

Description

  The present invention relates to a liquid ejection apparatus that ejects a liquid such as ink.

  In Patent Document 1, when the compressed image data is analyzed and it is determined that the white data area indicating the area where the image is not formed is equal to or larger than the specified size, the area is subjected to preliminary ejection for recovering the ejection performance. The present invention relates to an inkjet recording apparatus as a region to be performed.

JP 2009-255480 A

  In Japanese Patent Laid-Open No. 2004-228867, only an area where no image is formed is set and preliminary ejection is performed in the area, and how the preliminary ejection is specifically performed in the area is not specified. On the other hand, if the dot that is not related to image formation is not properly adjusted in which position and how it is formed, the sharpness of the image is impaired, and the image recording quality may be deteriorated.

  An object of the present invention is to provide a liquid ejecting apparatus that ejects liquid for recovery of ejection performance without impairing the sharpness of an image.

In order to achieve the above object, a liquid ejection apparatus according to an aspect of the present invention includes a liquid ejection head in which a plurality of ejection ports that eject liquid are arranged at equal intervals in one direction, and a conveyance direction that intersects the one direction. A transport unit that transports the recording medium relative to the liquid discharge head, and a unit distance corresponding to the recording resolution in the transport direction by the transport unit for each time required to transport the recording medium. Image dot formation control means for controlling the liquid ejection head based on image data so as to form an image dot constituting an image pixel by ejecting liquid from the liquid ejection head toward a recording medium to be conveyed When a non-image dot formation control means for forming a non-image dot which is not based on the image data by ejecting liquid toward the recording medium from the discharge port, wherein For outlet, from a first time point the the point at which the non-image dots are formed on the basis of the control point or the non-image dot forming control means and the image dots are formed on the basis of the control of the image dot formation control means , whether the image dots not forming period up to the time the next image dots are formed is equal to or greater than a predetermined time, and a sequentially determining means for each of the discharge ports, is determined by the determining means The non-image dot is performed both when the first time point is a time point when the image dot is formed and when the first time point is a time point when the non-image dot is formed. the formation control means, wherein a within a predetermined time or more to become the image dot not forming period, a time from a time point later than the first time, which has elapsed the predetermined time from the first time point To a non-image dots formed within the period in the period up to the point, along with the liquid toward the recording medium from the discharge port by the discharge once to form a non-image dot which is not based on the image data, the plurality of outlets a plurality of said according to the non-image dots are dispersed with respect to the transport direction, that controls the liquid discharge head.

  If a dot is formed immediately after the position where the image dot is formed, the boundary created by the image dot may be blurred. According to the present invention, dots are formed from the middle of an image dot non-formation period in which no image dots are formed. For this reason, since dots not related to image formation are always formed at positions away from the image dot formation position, the sharpness of the image is not impaired by the dots not related to image formation.

1 is a schematic plan view of an ink jet printer according to an embodiment of the present invention. It is a top view of the head main body shown in FIG. It is an enlarged view of the area | region enclosed with the dashed-dotted line shown in FIG. FIG. 4 is a partial cross-sectional view taken along line IV-IV shown in FIG. 3. It is an enlarged view of the area | region enclosed with the dashed-dotted line shown in FIG. It is a functional block diagram of the control apparatus shown in FIG. It is the figure which showed an example of the non-image dot by the image dot formed on the paper regarding a some discharge port based on control by the control apparatus of FIG. 6, and preliminary discharge. It is a figure which shows the relationship between the image dot formed on a paper regarding one discharge port, and image data corresponding to this, Image data is changed by the process of the control apparatus of FIG. It is also a figure which shows the condition where is inserted. 7 is a flowchart showing a series of processes performed by the control device of FIG. 6. It is a figure which shows the test image etc. which are used when acquiring the various settings used in the control apparatus of FIG.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

  The inkjet printer 101 includes a paper feeding unit that stores and supplies paper P, a transport unit that transports the paper P, an image forming unit that forms an image on the paper P, and a paper discharge unit that stores the paper P after image formation. Arranged along the paper transport path. Among these, the conveyance part is mainly comprised from the conveyance unit 20, as shown in FIG. The image forming unit includes four inkjet heads 1 (hereinafter referred to as head 1), one precoat head 2 (hereinafter referred to as head 2), and a control device 16. When image formation is performed, ink and a transparent precoat liquid are respectively ejected from the heads 1 and 2 onto the paper P transported by the transport unit 20.

  As the precoat liquid component, a pigment ink is used for aggregating pigment pigments, and a dye ink is used for depositing dye pigments. The precoat liquid is prepared by appropriately selecting a polyvalent metal salt such as a magnesium salt or a calcium salt in addition to a cationic polymer such as a diallyldimethylammonium chloride polymer or a diallylmethylammonium salt polymer using water as a main solvent. . When the ink lands on the region of the paper P to which such precoat liquid has been applied in advance, the polyvalent metal salt or the like acts on the dye or pigment that is the colorant of the ink to form an insoluble or hardly soluble metal composite or the like ( Agglomerated or precipitated). As a result, the penetrating degree of the adhering colorant into the paper P is reduced, and the colorant is easily fixed on the paper P.

  As shown in FIG. 1, the transport unit 20 includes two belt rollers 6 and 7 and an endless transport belt 8 that is stretched between the rollers 6 and 7. The belt roller 7 is a driving roller, and is rotated by a driving force from a conveyance motor (not shown). When the belt roller 7 rotates, the conveyor belt 8 runs. The belt roller 6 is a driven roller and rotates as the transport belt 8 travels. The paper P placed on the surface 8a of the transport belt 8 is transported from the top to the bottom in FIG. In the present embodiment, the sub-scanning direction is a direction parallel to the conveyance direction of the paper P by the conveyance unit 20, and the main scanning direction is a direction orthogonal to the sub-scanning direction and along the horizontal plane. is there.

  The four heads 1 are line type heads each having the main scanning direction as a longitudinal direction, and eject black, magenta, cyan, and yellow ink droplets onto the paper P, respectively. Each head 1 has a head body 1a (see FIG. 2). The lower surface of the head body 1a is a discharge surface 1s in which a plurality of discharge ports 108 are opened (see FIG. 4). The head 2 has the same configuration as the head 1. The head 2 is disposed upstream of the four heads 1 with respect to the transport direction of the paper P. The heads 1 and 2 are arranged parallel to each other and adjacent to each other in the sub-scanning direction.

  Next, the control device 16 will be described. The control device 16 controls the operation of each part of the printer 101 and controls the operation of the entire printer 101. For example, the control device 16 controls the image forming operation based on image data supplied from an external device (such as a PC connected to the printer 101). Specifically, the control device 16 controls the transport operation of the paper P, the ink discharge operation synchronized with the transport of the paper P, the recovery operation of the discharge characteristics of the heads 1 and 2 (for example, the preliminary discharge operation), and the like. Details of the preliminary discharge operation will be described later.

  Detection results from a temperature sensor 31 and a humidity sensor 33 (detection means) installed in the printer 101 are input to the control device 16. These detection results are used to adjust the length of the predetermined time T, which is a determination condition by the determination unit 155 described later.

  The control device 16 controls each operation of the paper feed unit (not shown), the transport unit 20, and the paper discharge unit (not shown) based on the recording command received from the external device. The paper feeding unit sends the paper P from the paper feeding unit to the transport unit 20. The transport unit 20 transports the paper P in the sub-scanning direction (paper P transport direction). When the paper P passes directly under the heads 1 and 2, the precoat liquid and ink are sequentially ejected from the ejection surfaces of these heads under the control of the control device 16, and a color image is formed on the paper P. At this time, the landing position of the pre-coated liquid droplets that land on the paper P first is adjusted to coincide with the landing position of the ink droplets that land next. When ink droplets land on the paper P, pigment aggregation occurs due to the pre-coated droplets that have landed first. As a result, the pigment remains near the surface of the paper P, and the quality of the image formed on the paper P is improved. The ink ejection operation is performed based on a detection signal from the paper width sensor 32 that detects the width of the paper P. The paper width sensor 32 is provided upstream of the head 2 in the transport direction, and detects that the leading edge of the paper P has passed below and the width of the paper P. Then, the paper P on which the image is formed is discharged to the paper discharge unit by the paper discharge unit.

  Next, the head main body 1a of the head 1 will be described in detail with reference to FIGS. Since the head body of the head 2 has the same configuration as the head body 1a, description thereof will be omitted below. In FIG. 3, for convenience of explanation, the pressure chamber 110, the aperture 112, and the discharge port 108 that are to be drawn with broken lines below the actuator unit 21 are drawn with solid lines.

  As shown in FIG. 2, the head body 1 a is a laminated body in which four actuator units 21 are fixed to the upper surface of the flow path unit 9. The actuator unit 21 includes a plurality of unimorph actuators corresponding to the pressure chambers 110 and selectively applies ejection energy to the ink in the pressure chambers 110. Although not shown, the head 1 is mounted on a reservoir unit that stores ink supplied to the flow path unit 9, a flexible printed circuit (FPC) that supplies a drive signal to the actuator unit 21, and an FPC. And a control board for controlling the driver IC.

  As shown in FIG. 4, the flow path unit 9 is a laminated body in which nine metal plates 122 to 130 made of stainless steel are laminated. As shown in FIG. 2, a total of ten ink supply ports 105 b communicating with the reservoir unit are opened on the upper surface of the flow path unit 9. As shown in FIGS. 2 to 4, a manifold channel 105 having an ink supply port 105 b as one end and a plurality of sub-manifold channels 105 a branched from the manifold channel 105 are formed inside the channel unit 9. Has been. Further, a plurality of individual ink flow paths 132 are formed in the flow path unit 9 from the outlets of the sub-manifold flow paths 105a through the pressure chambers 110 to the discharge ports 108 on the discharge surface 1s. A large number of ejection ports 108 formed on the ejection surface 1s are arranged in a matrix, and are arranged at an interval of 600 dpi, which is the resolution in the main scanning direction with respect to the main scanning direction.

  The ink flow in the flow path unit 9 will be described. As shown in FIGS. 2 to 4, the ink supplied from the reservoir unit to the ink supply port 105 b flows into the manifold channel 105 (sub-manifold channel 105 a). The ink in the sub-manifold channel 105 a is distributed to each individual ink channel 132 and reaches the ejection port 108 through the aperture 112 and the pressure chamber 110.

  Next, the actuator unit 21 will be described. As shown in FIG. 2, each of the four actuator units 21 has a trapezoidal planar shape, and is arranged in a staggered manner in the main scanning direction so as to avoid the ink supply ports 105b. Furthermore, the parallel opposing sides of each actuator unit 21 are along the main scanning direction, and the oblique sides of the adjacent actuator units 21 overlap each other in the sub-scanning direction of the flow path unit 9.

  As shown in FIG. 5, the actuator unit 21 is a piezoelectric actuator composed of three piezoelectric layers 141 to 143 made of lead zirconate titanate (PZT) ceramics having ferroelectricity. The uppermost piezoelectric layer 141 is polarized in the thickness direction. A plurality of individual electrodes 135 are formed on the upper surface of the piezoelectric layer 141. The individual electrode 135 faces the pressure chamber 110. An individual land 136 is provided at the tip of the individual electrode 135. A common electrode 134 formed on the entire surface of the sheet is interposed between the piezoelectric layer 141 and the lower piezoelectric layer 142. The common electrode 134 is equally applied with the ground potential in the region corresponding to all the pressure chambers 110. On the other hand, a drive signal is selectively supplied to the individual electrode 135 via the individual land 136.

  When the individual electrode 135 has a potential different from that of the common electrode 134, a portion sandwiched between the individual electrode 135 and the pressure chamber 110 is deformed with respect to the pressure chamber 110. In this way, the portion corresponding to the individual electrode 135 functions as an individual actuator. That is, a plurality of actuators corresponding to the number of pressure chambers 110 are built in the actuator unit 21.

  Here, a driving method of the actuator unit 21 will be described. In the actuator unit 21, the upper one piezoelectric layer 141 far from the pressure chamber 110 is a layer including a drive active portion, and the lower two piezoelectric layers 142 and 143 near the pressure chamber 110 are inactive layers. This is a so-called unimorph type actuator. For example, if the polarization direction is the same as the electric field application direction, the drive active portion (the portion sandwiched between both electrodes 134 and 135) contracts in a direction (plane direction) orthogonal to the polarization direction. At this time, there is a difference in distortion in the plane direction between the electric field application portion (driving active portion) and the lower piezoelectric layers 142 and 143, so that the entire piezoelectric layers 141 to 143 (individual actuators) are in the pressure chamber 110. Deforms to the side (unimorph deformation). As a result, pressure (discharge energy) is applied to the ink in the pressure chamber 110, and ink droplets are discharged from the discharge ports 108.

  In the present embodiment, a predetermined potential is applied to the individual electrode 135 in advance, and the individual electrode 135 is once set to the ground potential every time there is an ejection request, and then the individual electrode 135 is again set to the predetermined potential at a predetermined timing. A drive signal for applying a potential is supplied. At the timing when the individual electrode 135 becomes the ground potential, the piezoelectric layers 141 to 143 return to the original state, and the volume of the pressure chamber 110 increases as compared with the initial state (a state in which a voltage is applied in advance). Ink is sucked into the individual ink channel 132 from the channel 105a. Further, at the timing when a predetermined potential is applied to the individual electrode 135 again, the piezoelectric layers 141 to 143 are deformed so that the portion facing the electric field application portion protrudes toward the pressure chamber 110, and the volume of the pressure chamber 110 is increased. Since the pressure drops (the ink pressure increases), ink droplets are ejected from the ejection port 108.

  Next, the control device 16 will be described with reference to FIG. The control device 16 includes a CPU (Central Processing Unit), a program executed by the CPU and a ROM (Read Only Memory) that stores data used in these programs in a rewritable manner, and temporarily stores data when the program is executed. RAM (Random Access Memory). Each functional unit constituting the control device 16 is constructed by cooperation of these hardware and software in the ROM. As shown in FIG. 6, the control device 16 includes a conveyance control unit 161, an image data storage unit 162, a data writing unit 163, a head control unit 164, a preliminary ejection data creation unit 150, and a determination unit 155. have.

  The transport control unit 161 controls the operations of the paper feed unit, the transport unit 20, and the paper discharge unit so that the paper P is transported at a predetermined speed along the transport direction.

  The head controller 164 controls driving of each actuator included in the actuator unit 21 of each head 1. The head control unit 164 includes a drive data storage unit 165 that stores the written data as drive data for the actuator, and a drive unit 166 that outputs a drive signal for driving the actuator to each actuator. The drive unit 166 includes a driver IC that generates an amplified drive signal based on the drive data. The head controller 164 outputs a drive signal at a timing synchronized with the conveyance of the paper P based on the output of the paper width sensor 32.

  The image data storage unit 162 stores image data transferred from an external device. The image data indicates the dot size (any one of four levels of zero, small, medium, and large), the dot formation position, and the like for each ejection port 108 over a plurality of printing cycles. One printing cycle is the time required for the head 1 and the paper P to move relative to each other by a unit distance corresponding to the printing resolution in the paper transport direction. In the present embodiment, the large, medium, and small dot sizes are respectively formed with ink of a total discharge amount of 15 pl (picoliter), 10 pl, and 5 pl.

  The data writing unit 163 writes the image data stored in the image data storage unit 162 to the drive data storage unit 165 of the head control unit 164. Thereby, the head controller 164 can selectively control the driving of each actuator based on the image data. That is, the head control unit 164 and the data writing unit 163 constitute image dot formation control means for forming each image dot 81 (see FIG. 7) constituting pixels of the image 80 (see FIG. 7) on the paper P. Yes.

  Based on the image data stored in the image data storage unit 162, the determination unit 155 determines whether or not the image dot non-formation period, which is a period in which the image dots 81 are not continuously formed in the transport direction, is equal to or greater than the predetermined time T. Is determined for each discharge port 108. The determination unit 155 stores the magnitude of the predetermined time T set in association with conditions such as a temperature condition and a humidity condition. The predetermined time T corresponds to the frequency with which preliminary ejection is performed, and is set in advance according to the actual state in which the ejection performance of the ejection port 108 deteriorates due to ink thickening. A specific method for setting the predetermined time T will be described later. Based on the detection results from the temperature sensor 31 and the humidity sensor 33, the determination unit 155 acquires the magnitude of the predetermined time T according to these environmental conditions, and executes the above determination based on the predetermined time T. The predetermined time T may be set differently for each head 1 or head 2. The determination unit 155 includes a count addition unit 156 (addition unit). The count addition unit 156 counts and adds the number of pixels in which no image dot is formed in order to determine whether or not the image dot non-formation period is equal to or longer than the predetermined time T. Details of the count adder 156 will be described later.

Preliminary ejection data generating unit 150, with respect to each outlet 108 image dots not forming period is determined to be equal to or larger than the predetermined time T, the first time point or Rachodo predetermined time is the start time of the image dots not forming period toward the sheet P generates preliminary ejection data for performing one of the preliminary ejection within a period of the second time Tenma has elapsed, and outputs the drive data storage unit 165 of the head control unit 164. The one-time preliminary discharge here refers to preliminary discharge performed during one printing cycle, and includes, for example, one in which a plurality of drops of ink are continuously discharged from the discharge port 108 during one printing cycle. In one preliminary discharge, about 3 pl of ink droplets or precoat droplets are discharged, and one non-image dot 82 is formed on the paper P. The range of the two-dot chain line in FIG. 7 is an example in which the range of pixels corresponding to the first time point to the second time point is shown for each ejection port 108.

  The preliminary ejection data creation unit 150 includes a non-image dot formation period setting unit 151, a random number generation unit 152, and a non-image dot formation time point determination unit 153, and preliminary ejection data is generated by these units 151 to 153. Is done. The non-image dot formation period setting unit 151 sets a non-image dot formation period that is a period for forming one non-image dot 82 that is a dot that is not based on image data in one preliminary ejection (see FIG. 8). The non-image dot formation period is set to a period from the third time point to the second time point after the first time point. A setting method for setting the time point between the first time point and the second time point will be described later.

  The random number generation unit 152 generates a random number indicating at which point in the non-image dot formation period a non-image dot is to be formed. The non-image dot formation time point determination unit 153 determines the timing for forming the non-image dots based on the random number generated by the random number generation unit 152. The preliminary ejection data creation unit 150 generates preliminary ejection data for performing preliminary ejection at the timing determined by the non-image dot formation time determination unit 153 and outputs the preliminary ejection data to the drive data storage unit 165 of the head control unit 164.

  At this time, the preliminary discharge data creation unit 150 adjusts the preliminary discharge data once determined based on the random number from the following two viewpoints. The first point is to prevent the non-image dots from becoming conspicuous by preventing the non-image dots from the precoat liquid and the non-image dots from ink from overlapping each other. For this reason, the preliminary ejection data creation unit 150 compares the timing of preliminary ejection and the position of the ejection port 108 between the head 1 and the head 2 and compares the formation position of the non-image dots by the head 1 and the non-image dots by the head 2. When the formation position overlaps, the preliminary ejection data is adjusted so that they do not overlap. For example, the preliminary ejection timing of either one of the heads 1 and 2 is shifted, or any preliminary ejection is canceled.

  The second point is to prevent preliminary discharge from being performed in an area exceeding the width of the paper P so as not to stain the inside of the conveyor belt 8 and the printer 101. Therefore, the preliminary discharge data creation unit 150 adjusts the preliminary discharge data so as to cancel the preliminary discharge from the discharge port 108 corresponding to the position exceeding the width of the paper P based on the detection result from the paper width sensor 32. To do. In the ejection port 108 where the preliminary ejection is canceled, the ejection performance may be recovered by minutely vibrating the meniscus in a range where the liquid is not ejected.

  As described above, the head controller 144 can control the driving of each actuator based on the preliminary ejection data. That is, the head control unit 164 and the preliminary ejection data creation unit 150 cooperate to constitute a non-image dot creation control unit, and form a non-image dot 82 different from the image dot 81 on the paper P. In addition, when the image dot non-formation period is equal to or longer than the predetermined time T for each ejection port 108, non-image dots are formed by one preliminary ejection within the image dot non-formation period. Since the formation positions of the non-image dots follow random numbers as described above, the non-image dots formed with respect to the plurality of ejection ports 108 are dispersed in the transport direction as shown in FIG.

  For example, if the non-image dots 82 are formed at a fixed separation distance from the image dots 81, three image dots 81 are formed for the image dot group 81g arranged in the main scanning direction in FIG. Non-image dots are aligned along the main scanning direction. In this case, there is a high possibility that non-image dots are noticeable and visually recognized. On the other hand, according to the present embodiment, the non-image dots 82 formed for the image dot group 81g are distributed and arranged as in the non-image dot group 82g. For this reason, the non-image dots 82 are not noticeable.

  Hereinafter, a more specific flow of processing executed by the determination unit 155 and the preliminary ejection data creation unit 150 will be described with reference to FIG. First, the count addition unit 156 of the determination unit 155 resets the count for determination (S1). Next, the determination unit 155 determines whether or not image data on which an image dot is to be formed still remains in the image data storage unit 162 (S2). If it is determined that there is no remaining data (S2, No), a series of processing ends.

  If the determination unit 155 determines that there is still image data (S2, Yes), the image data is sequentially inquired for each ejection port 108 in the transport direction, and whether or not the image data indicates the formation of an image dot. Determine (S3). When that is not right (S3, No), the count addition part 156 of the determination part 155 counts the pixel number in which an image dot is not formed, referring image data in order (S4). Then, the determination unit 155 determines whether or not the count number has reached a predetermined number n (n: a natural number equal to or greater than 2) corresponding to the predetermined time T (S5; see FIG. 8). Here, the count being the predetermined number n corresponds to the image dot non-forming period reaching the predetermined time T. If it is determined that the predetermined number n has not been reached (S5, No), the process returns to S2. When the printer 101 has a plurality of modes having different sheet conveyance speeds, the predetermined number n corresponding to the predetermined time T varies depending on the mode. In this case, the determination unit 155 appropriately calculates the predetermined number n corresponding to the current mode.

  When the determination unit 155 determines that the count number has reached the predetermined number (S5, Yes), the non-image dot formation period setting unit 151 sets a non-image dot formation period within the image dot non-formation period (S6). . Specifically, the time point corresponding to the data that becomes n−m + 1, which is traced back by m−1 (m: a natural number smaller than n) from the data that has just reached n, is set as the third time point (FIG. 8). reference). Then, the non-image dot formation period is set from the third time point to the second time point.

  Next, the non-image dot formation time determination unit 153 determines the non-image dot formation timing according to the random number generated by the random number generation unit 152 (S7). Next, the preliminary ejection data creation unit 150 generates preliminary ejection data that instructs to form non-image dots at that timing (S8), and outputs the preliminary ejection data to the drive data storage unit 165. Then, the determination unit 155 updates the position where the next inquiry of the image data is started to a position immediately after the non-image dot formation position (S9). Thereby, for example, when an image dot is not formed immediately after the preliminary ejection is performed, the count is appropriately restarted from that point. Then, the count addition unit 156 resets the count (S1) and executes the processing from S2.

  A case where the above processing flow is applied to the image data of FIG. 8 will be described. In the example of FIG. 8, the leftmost data and the 18th data from the left (hereinafter, “from the left” is omitted and simply described as “18th”, etc.) are “2”. Data showing formation. The other data “0” is data indicating non-formation of image dots. The determination unit 155 starts an inquiry from the leftmost data. Since the leftmost data indicates image dot formation, the count adding unit 156 resets the count (S3, Yes → S1). From the second data, it is “0” indicating that image dots are not formed. From here, the count adding unit 156 continues to add counts (S2, Yes → S3, No → S4 → S5, No → S2). . When the fifteenth “0” is counted, the count reaches a predetermined number n (n = 14 in the example of FIG. 8) (S5, Yes). Here, the second data corresponds to the first time point, and the fifteenth data corresponds to the second time point.

  Then, the non-image dot formation period setting unit 151 sets the sixth data retroactive by m−1 (m = 10 in the example of FIG. 8) from the fifteenth data as the third time point. That is, the period corresponding to the 6th to 15th data is set as the non-image dot formation period (S6). Further, the non-image dot formation time point determination unit 153 determines the non-image dot formation timing to a timing corresponding to the 10th data among the 6th to 15th data by a random number (S7). The preliminary ejection data creation unit 150 generates preliminary ejection data (S8) and outputs the preliminary ejection data to the drive data storage unit 165, so that the tenth data of the image data stored in the drive data storage unit 165 becomes an image dot. Is changed from “0” indicating non-formation of “1” to “1” indicating formation of a non-image dot. Thus, preliminary ejection is performed to form the non-image dots 82 at a timing corresponding to this data. As described above, the preliminary ejection data creation unit 150 constitutes a data changing unit that changes image data so as to form non-image dots.

  Next, the count addition unit 156 resets the count and restarts the addition from the 11th data immediately after the 10th data changed to “1” (S9, S1 to S5). Thereafter, the data inquiry reaches the 18th and 19th data before the count reaches n, and in each case, the count is reset (S3, Yes → S1). Then, the count addition unit 156 starts counting again from the 20th data.

  Hereinafter, a method for setting the predetermined time T, which is a determination condition by the determination unit 155, will be described with reference to FIG. The predetermined time T is set by preliminarily ejecting ink or precoat liquid onto the paper P under predetermined environmental conditions to form a test image and evaluating the test image. As shown in FIG. 10, the test image I as an example of such a test image includes a plurality of solid images a <b> 1 extending almost over the entire area in the sub-scanning direction of the paper P. In addition, between the solid images a1, line rows b1 to b4 are formed that are arranged at equal intervals in the sub-scanning direction and are composed of a plurality of lines along the main scanning direction. Each of the line trains b1 to b4 includes 4 to 7 lines.

  Then, after forming such a solid image a1 and line rows b1 to b4, lines n1 to n7 made of image dots are formed at the same position downstream in the transport direction. As shown in FIG. 10, the lines n2, n4, and n6 located downstream of the solid image a1 are formed normally, but the lines n1, n3, and n5 located downstream of the line rows b1 to b3 are formed. In each dot constituting the line, the landing position is shifted downstream in the transport direction. This is because in the case of the line rows b1 to b3 where the number of ejections is smaller than that of the solid image a1, the ejection performance is deteriorated due to thickening of ink or the like at the ejection port 108.

  On the other hand, the line n7 located downstream of the line row b4 is normally formed. From this, it is understood that if the preliminary ejection is performed seven times with respect to the length of the paper P, a decrease in ejection performance due to thickening can be suppressed. Based on the above, the appropriate predetermined time T under the environmental conditions in which this test was performed is set to the time required to transport 1/7 of the length of the paper P. As an example, if the length corresponding to the length of the paper P is 7000 dots, the time required to transport the length corresponding to 1000 dots is an appropriate predetermined time T.

  The necessary frequency of preliminary ejection varies depending on environmental conditions such as temperature and humidity, and differences in heads, but an appropriate predetermined time T can be set by changing the test as described above. Since the predetermined time T corresponds to the frequency of the preliminary ejection, an appropriate frequency according to the condition is set. In general, the higher the temperature, the lower the viscosity of the ink or the like, so the frequency of preliminary ejection may be low, and the predetermined time T is set large. Similarly, the higher the humidity is, the more difficult the ink or the like dries, so the predetermined time T is also set larger. Also, different predetermined times T may be set depending on the types of ink and precoat liquid ejected by the head 1 and the head 2.

  Next, a setting method for setting which time point between the first time point and the second time point the third time point will be described with reference to FIG. The following setting method is mainly used when determining the determination condition of the head 1. The determination condition of the head 2 may be set to the same condition as the head 1 or may be set to a predetermined time T shorter or longer than the head 1. Since the non-image dots due to the transparent precoat liquid are hardly visually recognized, the non-image dots are not easily noticeable even if the frequency of preliminary ejection is high. Therefore, from this viewpoint, the predetermined time T of the head 2 may be set shorter than the predetermined time T of the head 1.

  As described above, since the line row b4 corresponds to the appropriate predetermined time T, the third time point is variously set in a range sandwiched between two lines of the line row b4, and the second time point from the third time point to the second time point. A non-image dot is formed up to the time point and the result is evaluated. For example, the candidate 1 indicates a case where the third time point is set at an intermediate position between the first time point and the second time point, and the candidate 2 has a length (predetermined time T) of 20 from the first time point to the second time point. % Indicates a case where the third time point is set after the first time point, and candidate 3 indicates a case where the third time point is set at the same time point as the first time point. For each candidate, the result of forming one non-image dot for each ejection port 108 so as to be dispersed in the transport direction between the third time point and the second time point is evaluated.

  According to an embodiment, in the case of candidate 1, since the range in which non-image dots are dispersed is narrow, the density of non-image dots is increased and is more noticeable than candidate 2. In the case of candidate 3, the non-image dot formed immediately after the first time point has blurred the boundary of the image formed by the image dot at the first time point. In the case of candidate 3, this is considered to be for preliminary ejection immediately after the first time point, that is, immediately after ejecting ink to form the line row b4. That is, immediately after ink ejection, the inside of the ejection port 108 does not progress so much and remains in a state where ink is easily ejected, so that the sharpness of the image based on the image data is likely to be impaired. Based on the above, the third time point of the present embodiment is set to at least one time point after the first time point. More preferably, according to the candidate 2, the third time point is set after the first time point by about 20% of the predetermined time T.

  Note that color difference may be used as a method for determining whether or not non-image dots are conspicuous. For example, a color difference ΔE between a blank portion on paper and a portion where non-image dots are dispersedly formed is measured by a colorimeter, and non-image dots are inconspicuous when ΔE = 1.4 or less, which can be recognized as a color difference by humans. The standard.

  According to the present embodiment described above, the third time point is set after the first time point, which is the timing immediately after the image dot is formed. Therefore, the preliminary ejection is not performed immediately after the image dots are formed, but after a certain amount of time. For this reason, as described above, the non-image dots formed by the preliminary ejection do not impair the sharpness of the image formed by the image dots. Further, the predetermined time T corresponding to the frequency of the preliminary discharge is set to an appropriate length for recovering the discharge performance according to each condition such as temperature and humidity. For this reason, preliminary ejection with an appropriate frequency according to the conditions is executed.

  The preferred embodiments of the present invention have been described above, but the present invention is not limited to the above-described embodiments, and various design changes can be made as long as they are described in the claims.

  In the above-described embodiment, it is assumed that image dots are not formed one by one in the image data, but the counting method may be variously changed. For example, when one unit of data includes information about a plurality of pixels, such as when image data is compressed, a plurality may be added to the count at a time.

  In the above-described embodiment, after determining the timing for forming the non-image dots, the determination unit 155 resumes the inquiry from the corresponding data immediately after the timing. However, the inquiry may be resumed from any data as long as the data corresponds to any time from the timing of forming the non-image dot to the second time.

  In the above-described embodiment, the non-image dots are dispersed in the transport direction according to the random number generated by the random number generation unit 152. However, non-image dots need only be made inconspicuous by this, and may be performed by a method other than using random numbers. For example, the position of the non-image dot may be calculated according to some mathematical formula as long as it is inconspicuous even if the position is regular. In addition, when the preliminary ejection data creation unit 150 temporarily sets the formation position of the non-image dots at a position separated from the first time point by a certain time, and the formation positions are aligned in a horizontal line with respect to the plurality of ejection ports 108, You may reset so that the formation position in any discharge port 108 may be shifted.

  The liquid discharge head according to the present invention is not limited to a printer, and can be applied to a liquid discharge apparatus such as a facsimile or a copier. Further, the number of liquid discharge heads applied to the liquid discharge apparatus is not limited to four, and may be one or more. The liquid discharge head is not limited to the line type, and may be a serial type. Furthermore, the liquid discharge head according to the present invention may discharge a liquid other than ink.

1 Inkjet head (head)
2 Precoat head (head)
16 Control device 81 Image dot 82 Non-image dot 101 Inkjet printer (printer)
108 Ejection port 150 Preliminary ejection data creation unit 151 Non-image dot formation period setting unit 152 Random number generation unit 153 Non-image dot formation point determination unit 155 Determination unit 156 Count addition unit T Predetermined time

Claims (12)

A liquid discharge head in which a plurality of discharge ports for discharging liquid are arranged at equal intervals in one direction;
Transport means for transporting the recording medium relative to the liquid discharge head along a transport direction intersecting the one direction;
Liquid is ejected from the liquid ejection head toward the recording medium transported by the transporting means for each time required for transporting the recording medium at a unit distance corresponding to the recording resolution in the transporting direction, and an image Image dot formation control means for controlling the liquid ejection head based on image data so as to form image dots constituting the pixels of
Non-image dot formation control means for forming a non-image dot not based on the image data by discharging liquid from the discharge port toward a recording medium;
The discharge port is a time point when the image dot is formed based on the control of the image dot formation control unit or a time point when the non-image dot is formed based on the control of the non-image dot formation control unit. A determination means for sequentially determining whether or not an image dot non-formation period from a time point to a time point when a next image dot is formed is equal to or longer than a predetermined time, for each of the ejection ports ;
The determination by the determination unit is performed in both cases where the first time point is a time point when the image dot is formed and when the first time point is a time point when the non-image dot is formed. I,
The non-image dot formation control means is
Wherein A within a predetermined time or more to become the image dot non-forming period, said from the time after the first time point, which is the period from the first time point to the second time point is a time when the predetermined time has elapsed non During the image dot formation period, liquid is ejected once from the ejection port toward the recording medium to form non-image dots that are not based on the image data, and a plurality of the non-image dots associated with the plurality of ejection ports. so they dispersed with respect to the conveying direction, the liquid ejecting apparatus according to claim and Turkey controls the liquid discharge head. The determination means is
An adding means for sequentially inquiring the image data along a direction corresponding to the transport direction, adding the number of pixels on which the image dots are not formed to the count, and resetting the count when forming the image dots 2. The liquid according to claim 1, wherein the image dot non-formation period is determined to be equal to or longer than the predetermined time when the count is n (n: a natural number equal to or greater than 2). Discharge device. The non-image dot formation control means is
When the determination unit determines that the image dot non-formation period is equal to or longer than a predetermined time, the count is nm + 1 (m: from the time point in the image dot non-formation period corresponding to the time point when the count is n. 3. The liquid ejection apparatus according to claim 2, wherein a period up to a time point in the image dot non-formation period corresponding to a time point that is a natural number smaller than n is set as the non-image dot formation period. The adding means is
When the count becomes n, the count is reset, and in the image data, the inquiry of the image data is started from the data next to the data corresponding to the time when the non-image dot is formed. The liquid ejection device according to claim 2 or 3. The image data further includes data changing means for changing the data corresponding to the time of forming the non-image dots to data indicating that the non-image dot formation control means forms the non-image dots,
5. The liquid ejection apparatus according to claim 1, wherein the non-image dot formation control unit forms the non-image dots based on the image data. A random number generating means;
6. The liquid according to claim 1, wherein the non-image dot formation control unit determines a time point at which the non-image dot is formed based on a random number generated by the random number generation unit. Discharge device. A detection means for detecting at least one of temperature and humidity;
The liquid ejection according to claim 1, wherein the non-image dot formation control unit sets a length of the non-image dot formation period according to a detection result of the detection unit. apparatus.   The liquid ejecting apparatus according to claim 1, wherein the non-image dot formation control unit sets the length of the predetermined period according to a type of liquid. The liquid discharge head is
A first discharge head that discharges the first liquid, and a second discharge that discharges a second liquid that is disposed upstream of the first discharge head in the transport direction and contains a component that aggregates or precipitates with the first liquid. Including the head,
The first discharge head and the second discharge head are both in the direction along the recording surface of the recording medium and perpendicular to the recording medium conveyance direction by the conveying means during recording on the recording medium. A line-type head that does not move,
The non-image dot formation control means is
The non-image dots related to the first discharge head and the non-image dots related to the second discharge head are both formed within the non-image dot formation period and formed at different positions on the recording medium. The liquid ejecting apparatus according to claim 1, wherein the liquid ejecting head is controlled as described above. The liquid discharge head is
A first discharge head that discharges the first liquid, and a second liquid that is disposed upstream of the first discharge head in the transport direction and discharges a transparent second liquid containing a component that aggregates or precipitates by the first liquid. 2 discharge heads,
The non-image dot formation control means is
The length of the non-image dot formation period is set so that the non-image dot formation period related to the second ejection head is shorter than the non-image dot formation period related to the first ejection head. Item 10. The liquid ejection device according to Item 1-9. The liquid discharge head is configured to discharge a plurality of types of droplets;
11. The liquid ejection according to claim 1, wherein the non-image dot formation control unit controls the liquid ejection head so as to form the non-image dots with the smallest droplet. apparatus. The liquid discharge head has a plurality of discharge heads for discharging a plurality of different liquids;
The liquid ejecting apparatus according to claim 1, wherein at least one of the predetermined time and the length of the non-image dot forming period is different for each of the ejection heads.

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